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Original question:

TMS320C6655: single DDR3 Layout constraint define

TMS320C6655: Routing Rules – Address and Command Lines (SDRAMs) - Stub between term resistors to DDR and DSP

Daniel Hoasov Cohen
Intellectual 300 points
Part Number: TMS320C6655

Tool/software:

Hi Experts,

per document: DDR3 Design Requirements for KeyStone Devices.pdf

There is a request to keep stubs less than 80mils between Fly-by group of address and command signals.

If a DDR routes to a DSP and also to term resistors, does the routing to term resistor count as a stub?

find the examples below:

  • +1
    TI__Guru 51695 points

    Yes - but I don't think its expected to be included in the highlighted recommendation.  The stubs to the memory devices have capacitive loading and create reflections.  The stub to the termination point affects the waveform differently.  I would still recommend trying to minimize the stub lengths to the termination.